The problem of sound pick up in a large room is typically accomplished by the use of multiple, directional microphones. In such instances a fixed installation or a main unit with wired auxiliary microphones is used. The possibility of providing an ad-hoc variety of audio devices within a room is only possible with significant user interaction. With the advent of wireless conference units the addition of wired auxiliary units becomes problematic.
With the advent of IP networks for multimedia it now becomes possible to have audio and video devices that work together in the same room. Again providing ad-hoc set-ups with minimal user interaction is desirable.
One method of providing for the use of several devices in the same room is to use some automatic detection scheme. Hopper et al. U.S. Pat. No. 5,493,283 suggests using an array of fixed infrared transponders that would automatically detect an infrared badge on the mobile user. Given that infrared light is generally confined to a room, this scheme allows location of all the mobile badges within the same room. However, the badges themselves are not capable of network communication with each other, nor do they interact any further with the fixed transponders.
Active Bat (1) proposed by Harter et al. (A. Harter et al., “The Anatomy of a Context-Aware Application,” Proc. 5th Ann. Int'l Conf. Mobile Computing and Networking (Mobicom 99), ACM Press, New York, 1999, pp. 59-68) discloses a similar application to Hopper et al., but uses mobile units (BATS) that respond to an RF signal by emitting an ultrasonic pulse. A base station periodically transmits a radio message containing a single identifier, causing the corresponding BAT to emit a short unencoded pulse of ultrasound.
Radio means have also been proposed, as the infrastructure is generally available. Some examples are Coffy in United States Patent publication no. 2004/003098, Williams and Needham U.S. Pat. No. 6,720,922, Stewart in U.S. Pat. No. 6,697,018 or Bahl et al in U.S. Pat. No. 6,799,047. These all require an array of fixed transponders with known locations. In order to use the radio frequency schemes to determine if two devices are within the same room, one must determine the distance between the mobile device and the fixed transponder. Using this information and a detailed floor plan one can then determine if a mobile user is within a certain room and if two devices are within the same room. Obviously this requires a great deal of user information to be entered in a database thus defeating the ad-hoc nature of the set-up.
To overcome this hybrid schemes have been proposed such as the “Cricket” locating scheme by N. B. Priyantha, A. Chakraborty, and H. Balakrishnan, “The Cricket Location-support System,” Proc. 6th Ann. Int'l Conf. Mobile Computing and Networking (Mobicom 00), ACM Press, New York, 2000, pp. 302-43k, the “Dolphin” scheme by Y. Fukuju et al, “DOLPHIN: An Autonomous Indoor Positioning System in Ubiquitous Computing Environment,” IEEE Workshop on Software Technologies for Future Embedded Systems, pp. 53-56, May 2003, the “Beep” scheme by Mandal et al. , “Beep: 3D Indoor Positioning Using Audible Sound.” Proc. IEEE Consumer Communications and Networking Conference (CCNC′05), Las Vegas, January 2005, as well as Rodman in United States Patent publication no. 2002/0101918. In these a radio frequency and audio system are combined. The basis of these is that the radio frequency part synchronizes and provides a control structure to the location of the mobile device. The acoustic signal is then used to determine the actual location of the device. Since building elements (walls, floors, ceiling and windows) are generally opaque to high frequency sound this easily allows one to locate users within the same room. Except for Rodman these schemes all require a fixed array of transponders and thus suffer from the same infrastructure costs of Hopper's infrared Active badge and the ultrasonic Active Bat.
Rodman teaches a more ad-hoc system by augmenting an existing radio frequency linked device with an acoustic discrimination analysis scheme to determine if two devices are within the same room. The audio signal must be sampled concurrently, converted to a digital representation, this digital data be transmitted via radio frequency to the location of the signal analysis processor where the data from the pair of devices is analyzed by the said processor. A discrimination analysis is performed which enables one to determine if the pair of signals is within the same room thus indicating that the devices are within the same room. However, this scheme requires a dedicated radio frequency link for the transport of the digitized audio signals and synchronization of the sampling. It thus cannot operate without this element. Furthermore it requires a “signal analysis processor”. In most radio frequency unlicensed bands, the devices used require pairing to achieve the level of density and security required. This is very difficult to do if the devices are not in the same room so the usefulness of Rodman's scheme in a real system seems to be to detect if one has left the room and to do so requires quite an expensive audio device.